1. Field of the Invention
The present invention generally relates to rotary drum assemblies and, more particularly, is directed to a rotary drum assembly having rotary heads suitable for use with a recording and/or reproducing apparatus in which a signal is recorded on and/or reproduced from a recording medium having a tape-shaped configuration through the heads.
2. Description of the Prior Art
In the prior art recording and/or reproducing apparatus having rotary heads, there has been proposed a rotary drum assembly in which a rotary drum having the rotary heads attached thereto and a stationary drum are opposed to each other with a space therebetween, spiral grooves are provided on one of opposite surfaces thereof, and a tape serving as a recording medium, which is wrapped and transported around both the rotary and stationary drums, is floated from the peripheral surface of the drums by the air which is blown out from the spiral grooves with the rotation of the rotary drum.
In the thus structured rotary drum assembly wherein the spiral grooves are provided on one of the opposed surfaces of the rotary and stationary drums so far to float the tape from the surfaces thereof by the air blown out from the spiral grooves, a pressure P of the blowing out air can be represented by the following formula (1): EQU P .alpha.{3.multidot..mu..multidot..omega..multidot.(Ro.sup.2 -Ri.sup.2)/Pa.multidot.Cr.sup.2 } (1)
where
Pa: an atmospheric pressure PA1 .mu.: a coefficient of viscosity of air PA1 Cr: a clearance (a distance of the space between the drums) PA1 .omega.: an angular velocity of the rotary drum PA1 Ro: an outer diameter of the spiral grooves PA1 Ri: an inner diameter of the spiral grooves
According to the formula (1), it will be understood that the blowing-out air pressure P is (a) proportional to a relative velocity (angular velocity .omega.) of the rotary drum, (b) inversely proportional to the square of the clearance Cr between the drums, and (c) proportional to a difference between the respective squares of the outer diameter Ro and the inner diameter Ri of the spiral grooves.
Accordingly, an amount of the tape floating, that is, a floating distance of the tape from the drum surface due to the blowing-out air pressure can be adjusted by suitably setting these parameters.
However, by some reason or when some electric circuit arrangement or optical lens or the like of an optical type head is mounted on the rotary drum, the difference between the outer and inner diameters of the spiral grooves becomes smaller. Namely, in the rotary drum assembly having the optical type head, since it is desirable to arrange its objective lens closer to the outer periphery of the drum and to provide the space (clearance) forming the air blowing-out portion closer to the optical axis of the objective lens, a width of the opposed surfaces of the rotary and stationary drums forming the space (clearance) of the air blowing-out portions can not be made large. Thus, the length of the spiral grooves become shorter and so the air blowing-out pressure becomes smaller disadvantageously.